Reports.md: describe how we handle received reports

[olasitarska]

• [x] Information about rotation duty and how it is implemented
• [x] What kind of reports we receive
  • [x] From local reps
  • [x] From people asking for help
• [x] If response requires decision, we aim to respond with a quick acknolwedgment of received report in a couple of hours
  • [x] Add example response here -- we may use the last one I sent last weekend
• [x] If response doesn't require decision, we still aim to respond within couple of hours, but acknowledge the report, thank the reporter, say we're gonna keep it on file.